Transmute Rock, how does it work?

[Consensus]

How does this part of this spell work? to me it seems that by RAW it would turn rock into mud... and then the mud would instantly disappear.

Transmute Rock

5th-level transmutation
Casting Time: 1 action
Range: 120 feet
Components: V, S, M (clay and water)
Duration: Instantaneous

You choose an area of stone or mud that you can see
that fits within a 40-foot cube and that is within range,
and choose one of the following effects.
Transmute Rock to Mud. Nonmagical rock of any
sort in the area becomes an equal volume of thick and
flowing mud that remains for the spell’s duration.

[DivisibleByZero]

I'm sure it's just a typo.
There should have been a duration listed other than Instantaneous. Use whatever duration you like. I'd go with 1 minute or 1 hour, or something like that.

[Ninja_Prawn]

I'm sure it's just a typo.
There should have been a duration listed other than Instantaneous. Use whatever duration you like. I'd go with 1 minute or 1 hour, or something like that.

I can't find any errata. In 3.5, I believe the duration was permanent... Alternatively, I'd consider 10 minutes (concentration) fair: that's what I used for my version of Transmute Lava.

[Coidzor]

The mud is permanent, you'll have to adhoc a duration for how long it flows for, though. Which will probably vary based upon elevation and slope.

[Lombra]

I do believe that the last part is a mistake and that the effect is permanent, concentration free. Many istantaneous spells work like that.